Best tube preamplifier for under $15k

The best one under 15k is the one that sounds best to you. Asking others a question like this is like asking someone what’s the best tasting pie under $15.
People tastes differ not only in what they like to hear, but also in what they like to eat. 

One other unit worth checking out is the KR Audio P 135.  It is a 45 based preamp.  Really cool unit with an unbelievable soundstage.  I personally am intrigued by the idea of pairing this preamp with a Chord Ultima 6.  I think it would be an incredible combo.  

I am a KR Dealer but you guys should check out the review on this one.  Worth the read.  

Exemplar audio XP-2 (15 K) , in view of most, who have heard this preammp, is as good as most preamps up to 35 K. It has vishay naked resistors & Urushi capacitors. I compared it to the stock Wavac PRT1 & it definitely to my ears was overall more musical & better . I still have PRT1 , but modified all resistors to Audio Note Tantalum silver resistors & Electrolytic caps to Audio Note Kesai. ( No Other Caps to change) , Only then the PRT1 sounds superior.
I compared Exemplar XP-2 n my previous life, to CJ ACT 2 & preferred the XP-2
I improved XP-2 further by bypass Audio Note Silver caps
The rest of my system;
Speakers Giya 2, Power Amps; Audio-Music 833 MKII, Silver Ultima Mono blocks, Audio-Music 833 MKII, Silve editin Monblocks, Jadis JA80 25th Anniversay, Lamm 2.2 .
T/T; Roy Borgess / Kuzma 14 inch . Technics SL1000 with 3 tonearms ( the other 2 tonearms ; Axiom & SME5) . cartridges include Clearaudio Goldfinger Statement.
I mention the above system , to assure, who is reading this , I am qualified to have an opinion about Hi Fi ( I am X- Publisher of Hi Fi plus mag )

I got both Aesthetix Eclipse and Atma-sphere MP-1. Both are excellent tube preamp. Different character but both are superb performers.